I am using the standard conf: --lookup-gap 0 -g1 -I 8 --worksize 64
I have custom modified my bioses with a HEX editor to get low Vcore values and the card to still boot. But I think with Sapphire cards you can go pretty low using Trixx also.

Here is a list of Watt/Mhash/Mhz/Vcore's I am using:

4x 17,3Mhash @ 950Mhz/0.856V = 405W
4x 18.3Mhash @ 1000Mhz/ 0.880V = 445W
4x 19Mhash @ 1040/0.900V = 460W
4x 19.8Mhash @ 1080/ 0.920V = 480W

I am not using higher setting such as 1150Mhz because it demands too much voltage